Electric vehicles having a motor for running mounted in place of an engine (including vehicles having the motor for running operated by a fuel cell) have been developed and put to practical use. Further, hybrid vehicles having a motor for running mounted in addition to an engine have also been developed and put to practical use. Such a vehicle is provided with electrical equipment such as a battery for running that outputs driving electric power to the motor for running. The battery for running involves a chemical reaction at the time of charging/discharging and, therefore, it must be cooled to prevent battery degradation caused when the battery attains to a high temperature.
In view of such a problem, Japanese Patent Laying-Open No. 2004-001674 discloses a battery temperature control device that reliably cools an in-vehicle battery. The battery temperature control device is applied to a vehicle having a rear air conditioner unit, which is installed at a rear part of the vehicle and contains air temperature adjusting means for adjusting temperature of the air blown out to the vehicle compartment, and the device controls the temperature of in-vehicle battery. The battery temperature control device has a duct leading the air that has passed through the air temperature adjusting means to the battery, and the air led by the duct is supplied to the battery, whereby the battery temperature is controlled.
According to the laid-open application, by the battery temperature control device, it is possible, when cooling the battery, to lower the air temperature blown to the battery than in the conventional example in which air in the vehicle compartment is blown to the battery.
In the battery temperature control device disclosed in the laid-open application, a plurality of routes are formed, including a route through which the air in the chamber directly flows to the battery and a route for cooling the battery using the air cooled by the air conditioner. The flow rate of air cooled by the air conditioner, however, is limited by the temperature state in the compartment and state of operation of air conditioner. Therefore, the flow rate of air supplied to the battery may also be limited.
When the air flow rate is limited, the flow rate of air supplied to the battery may fluctuate. Further, the temperature of supplied air is lowered by the air conditioner and, therefore, variation in air temperature tends to be large. Consequently, dependent on the shape of battery housing, it becomes difficult to supply air of uniform temperature at uniform flow rate to the entire battery cells. Particularly, when the battery scale becomes larger, it becomes more difficult to supply air of uniform temperature at uniform flow rate to the entire battery cells. This results in increased temperature difference inside the battery.
Electrical equipment such as a battery consists of a plurality of components including battery cells. If temperature difference among the components increases, amount of charge may possibly be different from one battery cell to another, and it would be difficult to control amounts of charge of all battery cells within a predetermined range.